When I red your experience with your feet I remembered the same experience on a concrete pavement.
For a sundial my feelings would say: use for each quarter of an hour a separate piece of stone separated by a thin thermal insulator. In that way even the slightest heat differences might be able to feel.
Thibaud Chabot
At 18:34 02-07-2004, John Carmichael wrote:
Hello All:
I've been meaning to tell you about an experiment I did....
Several months ago, we recieved a photo of a sundial for the blind that used a glass sphere to focus sunlight on metal strips located around it. Each strip is a different hour. The sun heats the strip and you feel the time. (The maker warns that you have to be careful to avoid buring your fingers!) I thought it was a neat idea then forgot about it.
Well, one day I was barefoot on on our red brick patio and my feet were on fire since the bricks were so hot. But I had to cross the patio to get to the other side. Rather than putting on shoes, I discovered if I walked along the shadow edge cast from the roof eave, that it wasn't so hot. The temperature difference of the brick between the shadow umbra and the full sun was huge. Then I remembered the Sundial for the Blind. I wondered how accurate a finger would be in finding out where the center of the penumbra is. I was surprised that I was able to feel with my finger within 2 cms. where the penumbral center was! This is just about as precise as using a shadow sharpener!
So, you don't need the magnifying effects of a glass sphere in order to feel the temperature difference. The sun alone is strong enough.
This implies that you could build sundial for the blind without having to magnify the sunlight. But I imagine that it wouldn't work very well very early in the morning or very late in the afternoon since the sun is weak at these time. I don't know if it would work in the winter. Also, you'd have to make the sundial face out of some low thermo-cunductive material like stone, cement or ceramics. I don't think you could make one out of any metal. The gnomom would have to be a "sheet" gnomon and not a cable or rod gnomon. Monumental large designs would problably work best.
Not that anyone will ever make one. I just thought you'd be interested in the concept.
John Carmichael
John L. Carmichael
Sundial Sculptures
925. E. Foothills Dr.
Tucson AZ 85718
USA
Tel: 520-6961709
Email: [EMAIL PROTECTED]
My Websites:
Sundial Sculptures: http://www.sundialsculptures.com
Stained Glass Sundials: http://stainedglasssundials.com
Th. Taudin Chabot, home email: [EMAIL PROTECTED]
